Risks to the Environment from Ivermectin use on marine fish farms.

Ivermectin is a widely used veterinary and human medicine.  It is approved for use on a number of farm animals, but has never been formally approved for treating sea lice infestations on marine fish farms.  It was, for a period of time, used on marine fish farms under a set of rules known as the "Cascade principles" which allow vets to prescribe an unlicencend drug to "a small number of animals" where there is no equivalent licenced product.  It is questionable whether several tonnes of salmon in a marine fish farm constitute "a small number of animals", but this has not been tested in the courts.  More importantly, there are a number of other compounds that are now licenced for the same use, and these drugs have been through a full ecotoxicity assessment, using procedures laid down by MAFF Veterinary Medicines Directorate. So the loophole that allowed Ivermectin to be used is now closed and administration of Ivermectin to farmed fish is, in consequence, now a criminal offence.

It is therefore disturbing that in the most recent food surveillance information from VMD, 10% of salmon flesh samples contained residues of Ivermectin (see pages 11 and 17 of this Veterinary Medicines Directorate publication).

We issued the following press release on February 17, 1998, describing some of our published research on the toxicity of Ivermectin to marine life.  These conclusions about the environmental risks of Ivermectin in the marine environment still stand.

For more information, contact Dr Alastair Grant on 01603 592537 or Email: A.Grant@uea.ac.uk


A drug used in salmon farms poses serious risks to the marine environment, say researchers at the University of East Anglia.
Ivermectin is in widespread use for treating sea lice infestation of farmed salmon and has been approved by the Scottish Environment Protection Agency.

New research by Dr Alastair Grant and Andrew Briggs, of UEA’s world-rated School of Environmental Sciences, raises serious concerns about the environmental safety of this drug, although they say there are unlikely to be significant risks to humans from eating the salmon.

"Some large retailers have refused to sell fish treated with the drug, although ivermectin is widely used to treat parasitic infections in humans and domestic animals," said Dr Alastair Grant. "But we have found that it is highly toxic to marine life and could have long-lasting effects."

He and Andrew Biggs have greatly extended available data on the drug by measuring its toxicity to eleven species of marine and estuarine animals.  The two most sensitive - crustaceans which resemble small shrimps - begin to die at concentrations of four nanograms per litre - equivalent to one ounce of ivermectin in ten thousand Olympic swimming pools.

"There are large variations in the sensitivity of species, and it is unlikely that we have found the most sensitive ones," said Dr Grant.  "Serious but non-lethal effects normally occur at concentrations substantially lower than those which are lethal."
Ivermectin is administered by mixing it with the salmon food, and most is rapidly excreted. Treated food is fatal if consumed by brown shrimps, and the same is almost certainly true of fish faeces.

The UEA researchers  have found species two thousand times more sensitive than brown shrimps - mobile scavengers which eagerly eat salmon pellets and faeces.

"Very little is known about ivermectin’s persistence or ecological effects in the sea lochs where salmon farms are located.  We do know that it is highly toxic to marine life and is introduced in a form that places other organisms at high risk of exposure," said Dr Grant.

The drug breaks down very slowly in the dark, so may persist for several months in marine sediments. So the available information raises significant concerns about the environmental safety of ivermectin.

"Until its environmental effects in the field are better understood, it is difficult to justify the continued release of ivermectin into what are some of the most pristine marine environments in the British Isles," he concludes.


1. For more information, contact Dr Alastair Grant on 01603 592537 or
Email: A.Grant@uea.ac.uk

2. The research has been published in Marine Pollution Bulletin.

Submission to Scottish Office consultation exercise on ivermectin
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